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PDF LTC3446 Data sheet ( Hoja de datos )
| Número de pieza | LTC3446 | |
| Descripción | Monolithic Buck Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC3446 (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
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FEATURES
n High Efficiency Triple Step-Down Outputs from a
Single Input Supply
n 1A Synchronous Buck Regulator Provides Main
Step-Down Output and Powers Two 300mA
VLDO™ Linear Regulators
n Output Voltages as Low as 400mV (VLDO Outputs)
n Power Good Output
n Input Voltage Range: 2.7V to 5.5V
n Independent Internal Soft-Start for Each Supply
n Independent Enable Pin for Each Supply
n Low (140μA Typ) No-Load Quiescent Current with
all Outputs Enabled
n Constant Frequency Current Mode Operation
n 2.25MHz Switching Frequency Uses Small
Inductors
n Defeatable Automatic Burst Mode® Operation for
High Efficiency at Light Loads
n ±1.5% Reference Accuracy
n Overtemperature Protection
n Thermally Enhanced 4mm × 3mm 14-Pin DFN
Package
APPLICATIONS
n Low Power Handheld Devices
n Low Voltage and Multivoltage Power for Digital
Logic, I/O, FPGAs, CPLDs, ASICs and CPUs
LTC3446www.DataSheet4U.com
Monolithic Buck Regulator
with Dual VLDO Regulators
DESCRIPTION
The LTC®3446 combines a synchronous buck DC/DC con-
verter with two very low dropout (VLDO) linear regulators
to provide up to three stepped-down output voltages from
a single input voltage. The input voltage range is ideally
suited for Li-Ion battery-powered applications, as well
as powering low voltage logic from 5V or 3.3V rails. The
output voltage range extends down to 0.4V for the VLDO
regulators and 0.8V for the buck.
The 1A synchronous buck converter provides the main
output with high efficiency, typically 85%. The two 300mA
VLDO regulators can run off the main output to provide
two additional lower voltage outputs. A built-in supply
monitor provides a power good indication.
The buck converter switches at 2.25MHz, allowing the use
of small surface mount inductors and capacitors. Constant
frequency current mode operation produces controlled
output spectrum and fast transient response. A mode-
select pin allows automatic Burst Mode operation to be
enabled for higher efficiency at light load, or disabled for
lower noise operation down to very light loads. The two
VLDO regulators are stable with ceramic output capacitors
as small as 1μF.
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
VLDO is a trademark of Linear Technology Corporation. All other trademarks are the property
of their respective owners. Protected by U.S. Patents including 5481178, 6611131, 6304066,
6498466, 6580258.
TYPICAL APPLICATION
VIN
2.9V TO 5.5V
22μF
X7R
DIGITAL
CONTROL
VIN SW
BUCKFB
LTC3446
LVIN
PGOOD LVOUT1
MODESEL
ENBUCK
ENLDO1 LVFB1
ENLDO2
1000pF
3.3k
ITH
LVOUT2
LVFB2
GND
3446 TA01
L1
1.8μH
59k
47.5k
110k
40.2k
80.6k
40.2k
22μF
X7R
VOUT
1.8V
400mA MAX
2.2μF
X7R
VOUT
1.5V
300mA MAX
2.2μF
X7R
VOUT
1.2V
300mA MAX
L1: TOKO A960AW-1R8M
Buck Efficiency vs Buck Load Current
100
Burst Mode
90 OPERATION
PWM
MODE
80
70
60
50
40
1
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
10 100
LOAD CURRENT (mA)
1000
3446 TA01b
3446fd
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LTC3446www.DataSheet4U.com
Buck Regulated Feedback Voltage
vs Temperature
808
806
804
802
800
798
796 VIN = 2.7V
VIN = 3.6V
794 VIN = 4.2V
VIN = 5.5V
792
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
3446 G01
LDO2 Regulated Feedback
Voltage vs Temperature
408
406
404
402
400
398
396 VIN = 2.7V
VIN = 3.6V
394 VIN = 4.2V
VIN = 5.5V
392
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
3446 G03
Maximum Peak Inductor Current
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
1.1 VIN = 5.5V
1.0
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
3446 G05
LDO1 Regulated Feedback
Voltage vs Temperature
408
406
404
402
400
398
396 VIN = 2.7V
VIN = 3.6V
394 VIN = 4.2V
VIN = 5.5V
392
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
3446 G02
Undervoltage Lockout Threshold
vs Temperature
2.50
2.45
2.40
UVLO RISING
2.35
UVLO FALLING
2.30
2.25
2.20
2.15
2.10
2.05
2.00
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
3446 G04
Oscillator Frequency
vs Temperature
2.50
2.45
2.40
2.35
2.30
2.25
2.20
2.15
2.10
VIN = 2.7V
VIN = 3.6V
2.05 VIN = 4.2V
VIN = 5.5V
2.00
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
3446 G06
3446fd
5
5 Page 
LTC3446www.DataSheet4U.com
OPERATION
can dramatically improve light load efficiency. The tradeoff
is higher output ripple than in constant frequency opera-
tion, as well as the presence of noise below the 2.25MHz
clock frequency.
If MODESEL were instead tied to VIN, pulse skipping mode
is selected. In this mode, the buck converter continues to
switch at a constant frequency down to very light loads
where it will eventually begin skipping pulses. Because
constant frequency operation is extended down to light
loads, low output ripple is maintained and any coupled
or radiated noise is at or higher than the clock frequency.
The tradeoff is lower efficiency compared to Burst Mode
operation.
Dropout Operation
When the input supply voltage decreases toward the
output voltage, the duty cycle increases to 100%, which
is known as the dropout condition. In dropout, the PMOS
switch is turned on continuously with the output voltage
equal to the input voltage minus any voltage drop across
the PMOS switch and the external inductor.
VLDO LINEAR REGULATOR OPERATION
The two micropower, VLDO (very low dropout) linear
regulators in the LTC3446 operate from input voltages as
low as 0.9V. Each VLDO regulator provides a high accuracy
output that is capable of supplying 300mA of output cur-
rent with a typical dropout voltage of only 70mV. A single
ceramic capacitor as small as 1μF is all that is required
for output bypassing. A low reference voltage of 400mV
allows the VLDO regulators to be programmed to much
lower voltages than available in common LDOs.
As shown in the Block Diagram, the VIN input supplies
the internal reference and biases the VLDO circuitry while
all output current comes directly from the LVIN input for
high efficiency regulation. The low per-VLDO quiescent
supply currents ILVIN = 4μA, IVIN = 80μA drop to ILVIN <
2μA, IVIN < 1μA in shutdown, are well-suited to battery-
powered systems.
Each VLDO includes current limit protection. The fast
transient response of the follower output stage overcomes
the traditional tradeoff between dropout voltage, quiescent
current and load transient response inherent in most LDO
regulator architectures. Overshoot detection circuitry is
included to bring the output back into regulation when
going from heavy to light output loads (“load-dump”
handling).
POWER GOOD CIRCUIT OPERATION
The LTC3446 has a built-in supply monitor. The feedback
voltage of each enabled supply is monitored by a window
comparator to determine whether it is within 8% of its
target value. If they all are, then the PGOOD pin becomes
high impedance. If no supply is enabled, or if any enabled
supply is more than 8% away from its target, then the
PGOOD pin is driven to ground by an internal open-drain
NMOS.
The PGOOD pin may be connected through a pull-up
resistor to a supply voltage of up to 5.5V, independent of
the VIN pin voltage.
3446fd
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3446.PDF ] | |
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